The present invention relates to a method or an apparatus for detecting fish schools of, for example, bonito, yellow-tail, a hair-tail, sardine, mackeral or tuna moving close to the surface of the water. Fish schools of these kinds are detected by locating a bird or birds such as a sea swallow or a booby gannet, etc., flying thereover.
A prior art method has used a pair of binoculars to find the birds. The prior method has presented the following disadvantages:
(1) The detectability of birds by the use of a pair of binoculars is limited to within the range of 6 or 7 miles, even under the most favourable weather conditions.
(2) The birds can not be found in rainy weather, in a dark environment or in dense fog.
(3) Close collaboration is required between the observer of the birds and the ship operator, when the birds found are followed.
(4) When a plurality of groups of the birds are found, the judgement to follow which group of the birds first is difficult to make, since the range to the discovered birds from the ship can not be accurately measured.